The invention relates to a wiper blade, in which a metal strip is used as the tilting bar, as well as to the metal strip itself.
Wiper blades for motor vehicles or aircraft are subjected to great mechanical stresses, on the one hand because of dust, insect pieces and other hard dirt particles, which roughen the glass surface to be cleaned, and on the other hand by the tilting stress, which during the wiping process continuously changes directions, and is constant in the rest position because of the continuing contact pressure with the glass panel. Added to the mechanical stresses are chemical and environmental effects, for example because of ozone, oil and alcohol and/or detergents in the windshield washer fluid.
Wiper blades with appropriate profiles (or cross sections) are as a rule continuously produced by means of extrusion or co-extrusion of vulcanizable polymer mixes. Following extrusion, the ropes are vulcanized to form elastomers and are cut to the required length. The wiper blades have a wiper head (also called base element or back), by means of which the wiper blade is fastened in the hoop system of the windshield wiper. On its side facing the glass panel, the wiper head makes a transition into a tilting bar, which is also called neck, hinge or folding bar, and which connects the wiper head with the wiper lip. In actual operation of the windshield wiper, the latter acts as the actual functional element of the wiper blade and keeps the glass pane clear of water. The tilting bar is the portion of the wiper blade which is mechanically stressed the most and as a rule determines the service life of the wiper blade. When produced by means of the extrusion or co-extrusion process mentioned, it consists of an elastomeric polymer material. Depending on the height of the tilting bar and the design of the surfaces of the wiper head and the wiper lip, which are located opposite each other, the main cross-sectional axis of the wiper lip can diverge in the position of rest by up to 45xc2x0 from the vertical line on the glass panel. In the operational state the wiper lip follows the wiper head, because of which a tilting movement is required at each direction change. Therefore the main cross-sectional axis of the wiper lip (vertically on the glass surface in the state where it is not pressed against it) continuously changes its position during operation by approximately xc2x145xc2x0.
The elastomers of which the wiper blades customarily are made are created from vulcanizable mixtures of natural or synthetic polymers or copolymers, which are vulcanized with organic peroxides and/or sulfur to form an elastomer. Wiper blades made of only one elastomeric material, namely caoutchouc, or of a mixture of caoutchouc and chloroprene rubber, or of caoutchouc and a rubber of the diene type, such a butadiene rubber or styrene rubber, are mentioned as being part of the prior art, for example in DE-C2 35 27 093. Caoutchouc and other types of diene rubber also contain olefinic double bonds and are therefore sensitive to ozone. The tendency to ozonolysis, along with the formation of cracks, can be reduced by a treatment with a hypochlorite solution (xe2x80x9cchlorinationxe2x80x9d). But chlorination is damaging to a tilting bar made of caoutchouc and other rubber types of the diene type, because under continuous pressure stress it encourages permanent plastic deformation. The wiper blade is subject to such a stress both in the position of rest and in operation, because it is continuously pressed against the glass pane.
The wiper blade in accordance with the invention in DE-C2 35 27 093 essentially consists of another material, namely EPDM rubber, a mixed polymer of ethylene, propylene and a diene, which is vulcanized with peroxides. However, the elastic properties of EPDM rubber depend to a considerable degree on the temperature, the same as the previously mentioned elastomers. In blowing snow and at temperatures below the freezing point, EPDM rubber also becomes increasingly brittle and is then no longer a match for the changing tilting movements. Furthermore, EPDM rubber is not impervious to the desired degree to chemicals and working materials, such as fuels or oil, which swell the rubber and soften it, which leads to a premature wear of the wiper blade lip and encourages plastic deformations.
Accordingly, it is an object of the present invention to provide a wiper blade which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a wiper blade in which the wiper head and the wiper lip are composed of at least one elastomer, and the connecting tilting bar is an elastic, resilient metal strip.
The highly stressed metal strip as the tilting bar, which determines the function and service life of the wiper blade, is completely impervious to chemical and environmental effects, such as occur when it is used in accordance with its purpose. The metal strip does no show aging under the effects of ozone, visible light or UV radiation, and no plastic deformation under pressure strain. Therefore wiper blades in accordance with the invention remain functional for a longer time than wiper blades with elastomeric tilting bars in accordance with the prior art. The elastic properties of the metallic tilting bars are furthermore practically independent of the outside temperature.